Device to Device (D2D) Proximity-based Services (ProSe) refer to a set of features supporting device to device communication in the Enhanced Packet System (EPS). ProSe features include ProSe Direct Discovery, which enables proximate devices to discover each other and the services proved by each other, and ProSe Direct Communication. ProSe features can be used for public safety applications (e.g. mission critical push to talk (MCPTT)) and/or for commercial applications.
ProSe Direct Communication is a mode of communication whereby user equipments (UEs) can communicate with each other directly over the PC5 (UE to UE) radio interface via direct air-interfaces between two devices (also referred to as sidelink channels). This may be in contrast to the radio interface between a UE and the base station (or the rest of the network), which may also be referred to as Uu.
For public safety-specific usage, ProSe Direct Communication is facilitated by the use of ProSe User-to-Network Relays (UNRs), which are UEs that act as relays between the network (e.g., an Evolved Universal Terrestrial Radio Access Network (E-UTRAN)) and one or more UEs not served by the network (e.g., to provide network based services to UEs which are out of network coverage). Also, ProSe Direct Communication between two UEs not served by the network and out of each other's transmission range may be facilitated by a ProSe UE-to-UE Relay (UUR).
Similar reference numerals may have been used in different figures to denote similar components.